1. Field of the Invention
This invention relates generally to methods for diagnosis and treatment of lung disease.
2. Description of the Related Art
Chronic obstructive pulmonary disease (COPD), including emphysema and chronic bronchitis, is a significant medical problem currently affecting around 16 million people in the U.S. alone (about 6% of the U.S. population). In general, two types of diagnostic tests are performed on a patient to determine the extent and severity of COPD: 1) imaging tests; and 2) functional tests. Imaging tests, such as chest x-rays, computerized tomography (CT) scans, Magnetic Resonance Imaging (MRI) images, perfusion scans, and bronchograms, provide a good indicator of the location, homogeneity and progression of the diseased tissue. However, imaging tests do not provide a direct indication of how the disease is affecting the patient's overall lung function and respiration. Lung function can be better assessed using functional testing, such as spirometry, plethysmography, oxygen saturation, and oxygen consumption stress testing, among others. Together, these imaging and functional diagnostic tests are used to determine the course of treatment for the patient.
One of the emerging treatments for COPD involves the endoscopic introduction of endobronchial occluders or endobronchial one-way valve devices (“endobronchial valves” or “EBVs”) into pulmonary airways to cause atelectasis (i.e., collapse) of a diseased/hyperinflated lung compartment, thus reducing the volume of that lung portion and allowing healthier lung compartments more room to breathe and perhaps reducing pressure on the heart. Examples of such a method and implant are described, for example, in U.S. patent application Ser. No. 11/682,986 and U.S. Pat. No. 7,798,147, the full disclosures of which are hereby incorporated by reference. One-way valves implanted in airways leading to a lung compartment restrict air flow in the inhalation direction and allow air to flow out of the lung compartment upon exhalation, thus causing the adjoining lung compartment to collapse over time. Occluders block both inhalation and exhalation, also causing lung collapse over time.
It has been suggested that the use of endobronchial implants for lung volume reduction might be most effective when applied to lung compartments which are not affected by collateral ventilation. Collateral ventilation occurs when air passes from one lung compartment to another through a collateral channel rather than the primary airway channels. If collateral airflow channels are present in a lung compartment, implanting a one-way valve or occluder might not be as effective, because the compartment might continue to fill with air from the collateral source and thus fail to collapse as intended. In many cases, COPD manifests itself in the formation of a large number of collateral channels caused by rupture of alveoli due to hyperinflation, or by destruction and weakening of alveolar tissue.
An endobronchial catheter-based diagnostic system typically used for collateral ventilation measurement is disclosed in U.S. Patent Publication No. 2003/0051733 (hereby incorporated by reference), wherein the catheter uses an occlusion member to isolate a lung segment and the instrumentation is used to gather data such as changes in pressure and volume of inhaled/exhaled air. Current state of the art methods for collateral ventilation measurement are disclosed in U.S. Pat. No. 7,883,471 and U.S. Patent Publication Nos. 2008/0027343 and 2007/0142742 (all of which are hereby incorporated by reference), in which an isolation catheter is used to isolate a target lung compartment and pressure changes therein are sensed to detect the extent of collateral ventilation. The applications also disclose measurement of gas concentrations to determine the efficiency of gas exchange within the lung compartment. Similar methods are disclosed in PCT Application No. WO2009135070A1 (hereby incorporated by reference), wherein gas concentration changes in a catheter-isolated lung portion allow collateral ventilation to be determined.
In addition to assessing collateral ventilation, there is an unmet need for quantifiably assessing air leaks (pneumothorax) within the lung. The lung is surrounded by a pleural cavity that ordinarily maintains a pressure that is slightly negative compared to atmospheric pressure. This slight negative pressure helps the lung inhale air from the atmosphere. An air leak occurs when a portion of the lung starts to leak air into the pleural cavity, thus removing the normal, negative pressure in the cavity and often leading to collapse of the lung. Such an air leak is caused by multiple factors such as disease, trauma to the lung, or as a complication of medical treatment.
Traditional methods of measuring air leaks have focused on a purely qualitative analysis of whether a leak exists rather than quantitative measures of the amount of leakage. Furthermore, the existing methods often rely on invasive means for diagnosis. For example, a Pleur-Evac® system (available from Teleflex Medical, www.teleflexmedical.com) relies on obtaining air from the pleural cavity via a catheter implanted into the pleural space via the chest. The air thus obtained from the pleural cavity is allowed to bubble through a fluid, and the quantity of the bubbles is correlated to the extent of the leak within the cavity. Such a method is inaccurate for multiple reasons. Since the value is obtained from the pleural cavity as a whole, there is no indication of where the air leak is located. The system also does not indicate the impact of the air leak on important parameters of lung function such as pressure or flow. Finally, the Pleur-Evac® system also does not indicate whether there are multiple air leaks and the rate of contribution of each air leak to the whole.
Therefore, a need exists for a more accurate and complete diagnostic method for quantifying air leaks within the lung. As discussed above, a need also exists for improved methods and systems to determine the presence of collateral channels and/or collateral ventilation. At least some of these objectives will be met by the embodiments described further below.